On engine-driven construction vehicles such as wheel loaders having separate motive (steering and braking) and implement (bucket and hoist) hydraulic power systems, it has heretofore been proposed to provide separate engine-driven hydraulic pumps for motive and implement applications, and to interconnect the respective systems for cross-assistance as required. Such prior art systems embody fixed displacement pumps coupled to the vehicle engine for providing an output which varies only with engine speed. Thus, at times of low hydraulic power demand, the pumps may provide more hydraulic power than required and thereby waste engine fuel, while the pumps may overload and stall the engine at times of high demand. It has thus been proposed to provide a hydromechanical cross-link between the respective hydraulic systems responsive to engine speed and pump flow to provide interconnection therebetween for mutual assistance at times of high demand on one system but not the other.